Does A Can or Suppresor Increase Back Pressure and Decrease Velocity??? Well????

In a gas gun we can agree that the rifle exhibits signs of being "over gassed" when suppressed--- but is this actually a higher chamber pressire-- or just a longer pressure curve? We know that a can "holds the pressure in the barrel longer" but im not convinced its due to a higher chamber pressure.
gas guns operate on a "balanced gas system" --- you need a certain VOLUME of gas at a certain PRESSURE for a certain length of TIME ( iirc this is Boyles law)...

So what we see as an increase in pressure, could be an increase in time or volume too.....without measuring chamber pressure there would be no way to be sure---- I think its just an increase of the same pressure over a linger time that causes these "over gassed ssymptoms"

We do know that when you "un cork" the barrel that gas pressure dramatically drops.

My chart I'm posting doesn't relate to cans, but it does show different pressures at chamber, gas port, and muzzle I'm reference to barrel length

View attachment 340200
Im thinking of pressure at the muzzle being higher w a can not in the chamber. The dwell time you show going up by length of bbl may just be the volume that a rifle tube holds and transports vs. a shorter gas tube. Yes, the gas gun is overpressured in the chamber for what it needs to slam the bolt back because the gas that would normally escape through the bbl gets forced through the port to the gas tube and slams the bolt back.

Too much pressure at the muzzle due to the can forces more gas into the gas port and back to the bolt.

I still think its muzzle pressure thats higher with a can vs no can.

Show me that same pressure profile you posted with and without a can.
Then we can see.
 
Well having that semi auto gas return tube in the data proves there is back pressure being added to the system when a can is installed. We wouldnt have that piece of the data or the puzzle if all we had was bolt guns in the data.

So I think its valuable for that reason for sure.
I disagree. A gas gun has a "vent"/port that drives the bolt. To my knowledge, the amount of blow back depends on the length from the gas port to the muzzle. Adding a can would increase length and time from port to "muzzle" wouldn't it? Whether you added a can or solid brake (barrel extension) would in effect result in more gas driven back before bullet exits and pressure drops. To me in this discussion on physics comparing a can on a bolt gun to a can effect on a gas gun ejection system is like trying g to compare a bicycle to a motorcycle
 
Im thinking of pressure at the muzzle being higher w a can not in the chamber. The dwell time you show going up by length of bbl may just be the volume that a rifle tube holds and transports vs. a shorter gas tube. Yes, the gas gun is overpressured in the chamber for what it needs to slam the bolt back because the gas that would normally escape through the bbl gets forced through the port to the gas tube and slams the bolt back.

Too much pressure at the muzzle due to the can forces more gas into the gas port and back to the bolt.

I still think its muzzle pressure thats higher with a can vs no can.

Show me that same pressure profile you posted with and without a can.
Then we can see.
Again I may be slightly off on my physics, but I can't see how pressure at the muzzle could ever be greater than in the chamber unless the muzzle was 100% obstructed.

I would think pressure would be relatively equal from chamber to where ever the base of the bullet inside the barrel is. Pressure would change as bullet is farther from its starting point, but it would be uniform in that space.
 
Mike and others that have chronographed have the right idea. measure and see the difference. I've never measured the difference, but it makes sense that "canned" shots are faster. The can has no physical effect on the bullet. It only deals with gas pressure. So if it slows down gas exit from barrel, the energy has to go somewhere. my take on is that since has to transfer energy somewhere, extends the time that the gas has a longer effect on the bullet.
I hope that this at least entertaining, because I am totaling talking out of my a**.
 
Again I may be slightly off on my physics, but I can't see how pressure at the muzzle could ever be greater than in the chamber unless the muzzle was 100% obstructed.

I would think pressure would be relatively equal from chamber to where ever the base of the bullet inside the barrel is. Pressure would change as bullet is farther from its starting point, but it would be uniform in that space.
No one has said that muzzle press is greater than chamber in fact one poster put up a nice graph of the profile of chamber pressure peaking and the decline along the barrel out to the muzzle. The only thing Im saying is when you add a can, that muzzle pressure you saw without a can wont be as low as it was before.

Call it restriction, call it a volume holding tank, call it whatever, but the gas does not escape as quickly as it did before the can. So in a gas gun we see this as gas has no where to go but into the gas port, down the gas tube, and into the chamber slamming the bolt back. Semi autos get over gassed when a can is added and the gas block which acts as a regulator valve has to be used to restrict or turn down too much gas from going to the chamber.
 
No one has said that muzzle press is greater than chamber in fact one poster put up a nice graph of the profile of chamber pressure peaking and the decline along the barrel out to the muzzle. The only thing Im saying is when you add a can, that muzzle pressure you saw without a can wont be as low as it was before.

Call it restriction, call it a volume holding tank, call it whatever, but the gas does not escape as quickly as it did before the can. So in a gas gun we see this as gas has no where to go but into the gas port, down the gas tube, and into the chamber slamming the bolt back. Semi autos get over gassed when a can is added and the gas block which acts as a regulator valve has to be used to restrict or turn down too much gas from going to the chamber.
Hard to respond when a person's terminology changes constantly
 
I use a can on a an 6.5 grendel AR. I use a BCG that is adjustable for gas pressure, like the ones from Bootleginc.com There are 4 settings, from Unsupressed to Suppressed,.. when I shot without an adjustable BCG, the brass was ejected forward, indicating over-gassed. I haven't done chrono testing on it so I am not sure, but it seems even in an semiauto AR platform, there is more gas pressure..
 
Love the thoughtfulness of OP and the replies in this thread.

My experience is only with medium to slow burning powders in hunting cartridges with high speeds punching heavy for caliber bullets as hard as I can get them. A couple of my cans exhibit none to very little increase in speed suppressed vs non-suppressed, barrel lengths 20-26 inches. The shorter battles seem to exhibit more increase with my longer ones shooting the same speed (0-5 fps) with or without cans: (28 nos and 30 Sherman with 26 in tubes). My 21 inch 6.5 prc and 21 inch 7saum exhibit roughly 30fps increase. My AR is the only one that has shown a decrease in velocity along with an increase in blowback pressure with a can - gas block adjustment and back to speed and cleaner (as much as possible in an AR) chamber. Two of those aforementioned rifles have no impact shift with suppressor vs non suppressed and those are the shorter barrels. Not sure if it's stiffer barrel or if the increase in speed offsets any decrease/change in harmonics/barrel whip.

This is a head scratcher for sure, definitely an academic measure, but real world applications are probably tough to pin down and mostly unnecessary since we have so many other variables to manage when shooting in different conditions the zero checks/adjustments and speed verifications are always a good idea.
 
Love the thoughtfulness of OP and the replies in this thread.

My experience is only with medium to slow burning powders in hunting cartridges with high speeds punching heavy for caliber bullets as hard as I can get them. A couple of my cans exhibit none to very little increase in speed suppressed vs non-suppressed, barrel lengths 20-26 inches. The shorter battles seem to exhibit more increase with my longer ones shooting the same speed (0-5 fps) with or without cans: (28 nos and 30 Sherman with 26 in tubes). My 21 inch 6.5 prc and 21 inch 7saum exhibit roughly 30fps increase. My AR is the only one that has shown a decrease in velocity along with an increase in blowback pressure with a can - gas block adjustment and back to speed and cleaner (as much as possible in an AR) chamber. Two of those aforementioned rifles have no impact shift with suppressor vs non suppressed and those are the shorter barrels. Not sure if it's stiffer barrel or if the increase in speed offsets any decrease/change in harmonics/barrel whip.

This is a head scratcher for sure, definitely an academic measure, but real world applications are probably tough to pin down and mostly unnecessary since we have so many other variables to manage when shooting in different conditions the zero checks/adjustments and speed verifications are always a good idea.
Shorter barrel may get a big boost from a long can that allows more gas push time on the bullet.
 
In the recent thread on the Satterlee, Audette, and OCW methods of load development and how I believe they are all related to barrel harmonics, the question has come up whether installing a suppressor increases back pressure or not and whether this cause a reduction in velocity.

I believe that the answer is that it can go either way and it all depends.

Here's some discussion and why:

My mental model of the pressure profile in the can is that as the bullet pushes and compresses air and possibly some gas from the explosion may leak by the bullet in the land grooves, into the can and it creates some back pressure vs. just going out the barrel into atmospheric 14.7 psig.

The pressure in the can especially in a longer bbl. has to be a bit higher than 14.7 psig atmospheric pressure. It just has to be mechanically, therefore it is exerting some amount of back pressure on the bullet before exit.

If you put a filter on the end of s garden hose what happens?

If you put mufflers on your car with baffles to silence the exhaust, what happens to your horsepower? Its backpressure. Thats why they use headers at the race track with no mufflers!!!

Flow rate slows due to back pressure. So I have no idea whether we can measure backpressure due to a can or how much it may slow muzzle velocity but I think it does. The only caveat I can think of is if you have a long bbl and a very slow powder, then the pressure curve or burn rate curve may have time to more fully develop giving added force from the chamber side of the explosion and increasing velocity that way. It would be similar to deeper bullet seating w crimps on a slow powder and long bbl.

So, perhaps there are boundary conditions where it can go both ways?

I do think it may be hard to measure the effects unless your ammo has a very low ES, say less than 5 fps.

IN short bbls. with fast powders, a can is maybe more likely to slow the bullet because there is no time for the burn curve to do anything more than its already doing....Burn curve = proxy for pressure curve or profile in the bbl.

In a long bbl w slow powder, maybe the velocity can increase because the back pressure delays bullet exit time in milli seconds that allows for a more complete powder burn to occur equals more force on chamber side of the bullet?

In Rifle Accuracy Facts the author has pictures of muzzle blast, pages (Photos of bullet exit p. 135, 136, 137)
He says Now we know that the muzzle blast pressure drops from 5000 psi to about 150 psi in 50 psec for the 6BR but we don't know just how the pressure drops off. So, there is pressure building in front of the bullet as I have been thinking. And though I have thought about burn rates with different pressure profiles in different length barrels, I did not realize a faster powder gives a lower muzzle pressure at exit as explained below.

He also says: The fact that a fast burning powder will result in a lower pressure at the muzzle than a slow burning powder was mentioned earlier. However, for the same muzzle velocity the faster burning powder will produce a higher chamber pressure. Nothing ever comes free in this business! I decided to test this contention by measuring the in-bore pressure at the muzzle using the strain gage method that we used to measure chamber pressure back in Chapter 2.

Since we are only interested in the comparison of muzzle pressures resulting from the two different powders, we don't have to go through the tedious calibration procedure used in measuring chamber pressure.
P146

So, the use of different burn rate powders and the length of the barrel may in fact have some bearing on what velocity we will see with the use of a suppressor and whether it goes up, or down or stays the same?

The author also drilled holes in a barrel and made it vented at the end, a muzzle brake of sorts. Here's what he found. It reduced muzzle velocity.
He does not explain why. But, if gas that could be used to propel the bullet is siphoned off, it makes sense I suppose.
A can is more confining than a muzzle brake of gas and more or less traps and vents it off after the bullet is gone. But, as I have stated above,
perhaps it can go either way with a can.......hard to say.

More quotes"

Well OK, did the muzzle ventilation help? It did. It reduced the average 5-
shot 100 yard group size from about 0.35" to 0.23" with match bullets and a
14" twist in the 6mm Remington rail gun. This is not as good as a top flight
6PPC HV gun or the 6BR rail gun which average in the high ones (i.e., 0.18").
The ventilated muzzle might be a good idea on sporters and long range magnum rifles, but there is talk about outlawing it in Hunter Class bench rest competition because of the increased muzzle blast on nearby shooters.

The muzzle blast pressure can be reduced by using a smaller grain or faster burning powder, longer barrels, lower chamber pressure, or a muzzle ventilator. How- ever, for a given case volume you have to give up velocity, or bullet weight,
or increase the maximum chamber pressure to obtain the same velocity. This usually means that one has to use a lighter load with the faster burning pow- der that won't fill the case, which may result in greater shot-to-shot velocity variations.
P 151

The muzzle blast pressure was measured using strain gages and it was deter-
mined that large cases (270 Win.) with relatively slow burning, large grained powder had a much larger muzzle blast pressure than relatively fast burning small grained powder. Muzzle blast pressure was also decreased with longer
barrels and ventilated muzzles. Muzzle ventilation was tried and it did reduce the muzzle blast pressure as expected and produced a significant reduc-
tion in group size. However, the type of muzzle venting that was used is a
difficult machining job that would be expensive to do in production.

Now from other sources I searched for:

This below says suppressors cause back pressure, although newer designs cause much less than what they once did. How and when it occurs is critical.

Most have little effect on bolt guns beyond heat transfer and a sticky bolt that is hard to lift. Gas guns are a different story. Increased back pressure causes increased bolt speed and can wreak havoc on function. Piston-driven systems are less susceptible, but can still be problematic. As a general rule, the shorter the barrel, the greater the effect on the gun's performance. Adjustable gas blocks help but remain an issue. Excess gas in the action can also affect reliability as the action can get fouled quickly. Rapid fire produces significant heat transfer to the weapon and can have an adverse effect on operation.

https://gundigest.com/gear-ammo/suppressor-effects


Might go either way depending on baffle design and where gas goes....
https://www.snipershide.com/shooting/threads/backpressure-and-suppressor-design.6938437/


No statistically significant impact.
https://www.thetruthaboutguns.com/ask-foghorn-does-a-silencer-effect-the-velocity-of-the-bullet/

Maybe we will learn something from this?

I believe now it can go either way depending on suppressor design, rifle barrel length, and powder burn rate, and your ability to measure
slight variations in velocity FPS within the quality of the ES and SD of the Ammo you are firing.
The projectile slams into the rifling with 60,000 Psig behind it, the resulting seal created between the carbon steel barrel and the much softer copper of the projectile is perfect. You simply don't have any discernible gas leakage, if you did then the barrel and suppressor are totally open to atmosphere. Nothing like your car muffler example.
I have a number of rifles with suppressors on the chronograph there's no noticeable changes in velocity. Point of impact can alter but that's harmonics in play.
Your premise is due to serious overthinking on a nonexistent problem.
 
The projectile slams into the rifling with 60,000 Psig behind it, the resulting seal created between the carbon steel barrel and the much softer copper of the projectile is perfect. You simply don't have any discernible gas leakage, if you did then the barrel and suppressor are totally open to atmosphere. Nothing like your car muffler example.
I have a number of rifles with suppressors on the chronograph there's no noticeable changes in velocity. Point of impact can alter but that's harmonics in play.
Your premise is due to serious overthinking on a nonexistent problem.
Rocketeer 77, you don't even understand gas blow by. At least , please try to be polite if you are going to be absolutely wrong.
Here's a picture with some captions to help you understand.

Figure 7- 1 3 shows a picture of the precursor spherical shock wave formed by the compressed air and blow-by ahead of the bullet. The bullet is about three inches back down the bore.

Figure 7-13- Shadowgraph photo showing the spherical precursor shock wave emerging from the bore. The precursor is formed by the compressed air and gas ahead of the bullet. The bullet is about three inches back in the bore.

1644622878009.png

All figures and photos excerpted from Rifle Accuracy Facts.

I hope you won't seriously overthink any premise I may make. Cause, if I am making a premise i.e., thinking, its
not always right, but the odds are I at least have half a clue.

Take care over there in New Zealand.
 
In the recent thread on the Satterlee, Audette, and OCW methods of load development and how I believe they are all related to barrel harmonics, the question has come up whether installing a suppressor increases back pressure or not and whether this cause a reduction in velocity.

I believe that the answer is that it can go either way and it all depends.

Here's some discussion and why:

My mental model of the pressure profile in the can is that as the bullet pushes and compresses air and possibly some gas from the explosion may leak by the bullet in the land grooves, into the can and it creates some back pressure vs. just going out the barrel into atmospheric 14.7 psig.

The pressure in the can especially in a longer bbl. has to be a bit higher than 14.7 psig atmospheric pressure. It just has to be mechanically, therefore it is exerting some amount of back pressure on the bullet before exit.

If you put a filter on the end of s garden hose what happens?

If you put mufflers on your car with baffles to silence the exhaust, what happens to your horsepower? Its backpressure. Thats why they use headers at the race track with no mufflers!!!

Flow rate slows due to back pressure. So I have no idea whether we can measure backpressure due to a can or how much it may slow muzzle velocity but I think it does. The only caveat I can think of is if you have a long bbl and a very slow powder, then the pressure curve or burn rate curve may have time to more fully develop giving added force from the chamber side of the explosion and increasing velocity that way. It would be similar to deeper bullet seating w crimps on a slow powder and long bbl.

So, perhaps there are boundary conditions where it can go both ways?

I do think it may be hard to measure the effects unless your ammo has a very low ES, say less than 5 fps.

IN short bbls. with fast powders, a can is maybe more likely to slow the bullet because there is no time for the burn curve to do anything more than its already doing....Burn curve = proxy for pressure curve or profile in the bbl.

In a long bbl w slow powder, maybe the velocity can increase because the back pressure delays bullet exit time in milli seconds that allows for a more complete powder burn to occur equals more force on chamber side of the bullet?

In Rifle Accuracy Facts the author has pictures of muzzle blast, pages (Photos of bullet exit p. 135, 136, 137)
He says Now we know that the muzzle blast pressure drops from 5000 psi to about 150 psi in 50 psec for the 6BR but we don't know just how the pressure drops off. So, there is pressure building in front of the bullet as I have been thinking. And though I have thought about burn rates with different pressure profiles in different length barrels, I did not realize a faster powder gives a lower muzzle pressure at exit as explained below.

He also says: The fact that a fast burning powder will result in a lower pressure at the muzzle than a slow burning powder was mentioned earlier. However, for the same muzzle velocity the faster burning powder will produce a higher chamber pressure. Nothing ever comes free in this business! I decided to test this contention by measuring the in-bore pressure at the muzzle using the strain gage method that we used to measure chamber pressure back in Chapter 2.

Since we are only interested in the comparison of muzzle pressures resulting from the two different powders, we don't have to go through the tedious calibration procedure used in measuring chamber pressure.
P146

So, the use of different burn rate powders and the length of the barrel may in fact have some bearing on what velocity we will see with the use of a suppressor and whether it goes up, or down or stays the same?

The author also drilled holes in a barrel and made it vented at the end, a muzzle brake of sorts. Here's what he found. It reduced muzzle velocity.
He does not explain why. But, if gas that could be used to propel the bullet is siphoned off, it makes sense I suppose.
A can is more confining than a muzzle brake of gas and more or less traps and vents it off after the bullet is gone. But, as I have stated above,
perhaps it can go either way with a can.......hard to say.

More quotes"

Well OK, did the muzzle ventilation help? It did. It reduced the average 5-
shot 100 yard group size from about 0.35" to 0.23" with match bullets and a
14" twist in the 6mm Remington rail gun. This is not as good as a top flight
6PPC HV gun or the 6BR rail gun which average in the high ones (i.e., 0.18").
The ventilated muzzle might be a good idea on sporters and long range magnum rifles, but there is talk about outlawing it in Hunter Class bench rest competition because of the increased muzzle blast on nearby shooters.

The muzzle blast pressure can be reduced by using a smaller grain or faster burning powder, longer barrels, lower chamber pressure, or a muzzle ventilator. How- ever, for a given case volume you have to give up velocity, or bullet weight,
or increase the maximum chamber pressure to obtain the same velocity. This usually means that one has to use a lighter load with the faster burning pow- der that won't fill the case, which may result in greater shot-to-shot velocity variations.
P 151

The muzzle blast pressure was measured using strain gages and it was deter-
mined that large cases (270 Win.) with relatively slow burning, large grained powder had a much larger muzzle blast pressure than relatively fast burning small grained powder. Muzzle blast pressure was also decreased with longer
barrels and ventilated muzzles. Muzzle ventilation was tried and it did reduce the muzzle blast pressure as expected and produced a significant reduc-
tion in group size. However, the type of muzzle venting that was used is a
difficult machining job that would be expensive to do in production.

Now from other sources I searched for:

This below says suppressors cause back pressure, although newer designs cause much less than what they once did. How and when it occurs is critical.

Most have little effect on bolt guns beyond heat transfer and a sticky bolt that is hard to lift. Gas guns are a different story. Increased back pressure causes increased bolt speed and can wreak havoc on function. Piston-driven systems are less susceptible, but can still be problematic. As a general rule, the shorter the barrel, the greater the effect on the gun's performance. Adjustable gas blocks help but remain an issue. Excess gas in the action can also affect reliability as the action can get fouled quickly. Rapid fire produces significant heat transfer to the weapon and can have an adverse effect on operation.

https://gundigest.com/gear-ammo/suppressor-effects


Might go either way depending on baffle design and where gas goes....
https://www.snipershide.com/shooting/threads/backpressure-and-suppressor-design.6938437/


No statistically significant impact.
https://www.thetruthaboutguns.com/ask-foghorn-does-a-silencer-effect-the-velocity-of-the-bullet/

Maybe we will learn something from this?

I believe now it can go either way depending on suppressor design, rifle barrel length, and powder burn rate, and your ability to measure
slight variations in velocity FPS within the quality of the ES and SD of the Ammo you are firing.
I know of some people using a 338LM, and that had higher velocity with a suppressor.
 

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